The operation of an engine using more than one fuel is known. Many of these systems try reduce the overall fuel cost by utilising a cheaper secondary fuel to displace the usage of a relatively more expensive primary fuel. Systems of this type can either be retrofitted to an existing engine or supplied as an integral part of the engine/vehicle by the manufacturer. There are a large variety of systems produced for the automotive market, particularly the light and heavy goods market, where the fuel costs comprise a significant cost for operators.
There are generally two types of system typically used.
The first type of system works by introducing a secondary fuel in addition to the primary fuel. The quantity of primary fuel is generally unchanged. These are generally known as ‘addition’ systems. The principle involved is that the introduction of the secondary fuel increases the power/torque of the engine and that an adaptation made either by the original engine control system or by the operator results in a net fuel cost saving. Some systems of this type also employ some crude forms of control in an attempt reduce the primary fuelling, typically by changing the inputs from sensor or modifying torque or speed control inputs.
There are several limitations of such addition systems. The amount of secondary fuel that can be introduced is limited by the ability of the engine to combust the secondary fuel, primarily due to a lack of oxygen, commonly known as “oxygen depletion” and the secondary fuel “quenching” the combustion of the primary fuel. Operation in this mode leads to poor fuel consumption and high emissions due to incomplete combustion and the pass through of un-burnt fuel products that exits the exhaust. The fuel saving generated is not guaranteed and can be negative as well as positive. Deliberate over-powering of an engine will cause it to operate outside of its normal operational. This will have negative implications in terms of manufacturer's warranty, insurance approvals, safety certification and potential engine life.
The second type of system works by introducing a secondary fuel in addition to a reduced quantity of the primary fuel. These are commonly known as ‘substitution’ systems. The principle involved is that both primary and secondary fuels are directly controlled and that both fuels when combusted simultaneously generate approximately the same power/torque as the original engine when operating only on the primary fuel.
The percentage of the two fuels employed gives rise to a further distinction between systems of this substitution-type. Systems which use a higher proportion of secondary fuel to primary fuel where the primary fuel is diesel and the secondary fuel is gaseous are known as diesel ignition gas engines. Systems which use a lower proportion of secondary fuel to primary fuel where the primary fuel is diesel and the secondary fuel is gaseous retain their classification as diesel engines.
Both types of substitution system are characterised in that they require a minimum of proportion of approximately 25% of secondary fuel to be employed for the system to be commercially viable. As similar figure is necessary for addition systems to be viable, assuming that they can be made to operate in a favourable mode that generates a net fuel cost saving.
U.S. Pat. No. 4,463,734 discloses a diesel engine in which increasing proportions of liquefied petroleum gas (LPG) are metered to the engine as power demand increases, starting from as little as 20% gas and increasing to about 80% gas, where the percentage is given in calorific value. U.S. Pat. No. 4,641,625 discloses a range of gaseous fuel in a liquid gas mixture of between 0 and 95% gas. U.S. Pat. No. 6,026,787 and US 2005/0205021 both disclose dual fuel engines, but without specifying the proportions of the fuels. WO 2008/036999 is directed to a dual fuel system and a dual fuel system assembly where liquid LPG and diesel are mixed and then distributed via the common rail to the combustion chambers. WO 2010/121306 relates to fuel systems for diesel engines. In particular, the invention relates to a dual fuel supply system for a diesel engine having an indirect-injection system. U.S. Pat. No. 5,408,957 discloses LPG (propane), natural gas, hydrogen gas, or the like, is continuously injected at substantially constant pressure into the air intake manifold, or air induction system, of a conventional internal combustion engine, the engine being electronically, or mechanically, controlled to adjust the air to liquid fuel mixture to a optimum value. U.S. Pat. No. 5,370,097 discloses a dual fuel control system for use with an internal combustion engine which controls the flow of liquid fuel alone or in combination with a gaseous fuel. US 2011/301826 discloses a conventional gasoline engine that is retrofitted to operate as a bi-fuel engine calibrated to burn hydrogen gas as a primary fuel and gasoline as a secondary fuel at various acceptable air fuel ratios while avoiding forbidden air fuel ratios. WO 99/30024 relates to a method for producing NOx reductants by injecting hydrocarbon into a diesel engine's combustion chamber during the expansion cycle.
WO 2009/115845 discloses the injection of a small amount of a secondary fuel having a shorter molecular structure than a primary fuel for achieving homogenous combustion. The shorter molecular structure of the secondary fuel is used as an accelerant to accelerate the chemical process and a range of between 5%-25% of the secondary fuel is disclosed. Moreover, both the supply of the primary and the secondary fuel are controlled.
Thus, existing dual-fuel systems have several limitations, such as requiring a minimum fraction of approximately 25% of secondary fuel and/or requiring that the ECU or primary fuel supply are controlled or adapted.
It is therefore desireable to overcome these limitations and/or produce an even greater improvement in fuel efficiency.
According to one aspect of the invention there is provided a method of improving the efficiency of a combustion engine, the method comprising: measuring a quantity of a primary fuel being supplied to the combustion engine; determining an operating state of the combustion engine; selecting a fuel mapping profile based on an operating state of the combustion engine; and determining from the fuel mapping profile an amount of a secondary fuel to be injected as a fraction of the measured quantity of the primary fuel.
According to another aspect of the invention there is provided a combustion engine comprising: a first sensor for measuring a quantity of a primary fuel supplied to the combustion engine; a second sensor for determining an operating state of the combustion engine; a controller selecting a fuel mapping profile based on an operating state of the combustion engine; and the controller determining from the fuel mapping profile an amount of a secondary fuel to be injected as a fraction of the measured quantity of the primary fuel.
According to yet another aspect of the invention there is provided a kit for retrofitting a combustion engine designed to combust a primary fuel, the kit comprising: a tank for holding a secondary fuel; an injector for injecting secondary fuel into the engine; a controller configured to receive: a first input indicating the quantity of the primary fuel being supplied to the engine, and a second input indicating an operating state of the engine; and wherein the controller is configured to select a fuel mapping profile based on the operating state and to determine from the selected fuel mapping profile, an amount of a secondary fuel to be injected by the injector as fraction of the measured quantity of the primary fuel.
According to yet another aspect of the invention there is provided a controller for controlling an injection of a second fuel into an engine supplied with a primary fuel, the controller comprising: a first input for receiving an indication of the quantity of the primary fuel being supplied; a second input for receiving an indication of an operating state of the engine; a memory for storing a plurality of fuel mapping profiles; a processor for selecting one of the fuel mapping profiles based on the second input and determining an amount of the secondary fuel to be injected as a fraction of the measured quantity of the primary fuel.
According to yet another aspect of the invention there is provided a method of improving the efficiency of a combustion engine, the method comprising: measuring a quantity of a primary fuel supplied to the combustion engine; and injecting an amount of a secondary fuel based on a fraction of the measured quantity of the primary fuel, wherein once a threshold quantity of the primary fuel is exceeded, the fraction of secondary fuel decreases as the quantity of primary fuel increases.
According to yet another aspect of the invention there is provided a method of improving the fuel efficiency of an internal combustion engine, the method comprising: measuring a quantity of a primary fuel supplied to the internal combustion engine; injecting an amount of a secondary fuel based on a fraction of the measured quantity of the primary fuel, the primary fuel having a larger molecular structure than the secondary fuel; splitting the primary fuel into smaller molecules using the secondary fuel.
Preferably or optionally, wherein the step of splitting comprises: a first splitting of the secondary fuel to produce radicals by compressing air that is combined with the secondary fuel; and a second splitting of the primary fuel by combining the radicals with the primary fuel.
According to another aspect of the invention there is provided a method of improving the fuel efficiency of an internal combustion engine, comprising the steps of measuring the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the amount by calorific value of the second fuel injected is limited to the Minimum Fraction where significant enhancement of combustion begins and the Maximum Fraction where the inefficiency of combusting the second fuel (for an engine designed to combust first fuel) significantly counters the enhancement effects.
According to yet another aspect of the invention there is provided a method of improving the fuel efficiency of an internal combustion engine, comprising the steps of measuring the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the amount of the second fuel injected is limited so that the mass of the combined fuels injected into the engine for a given level of performance is less than the mass of the first fuel needed to achieve the same level of performance when injected alone.
According to yet another aspect of the invention there is provided a system for improving the fuel efficiency of an internal combustion engine, comprising means for connection to the fuel supply system of the engine, means for measuring the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and means for supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the system comprises: a microprocessor for receiving signals from the measuring means and monitoring means; and wherein the microprocessor is adapted to calculate the quantity of the first fuel injected and produce and transmit a resultant signal to said means for supplying the second fuel.
According to one aspect of the invention there is provided method of improving the fuel efficiency of an internal combustion engine, the method comprising: measuring a quantity of a primary fuel supplied to the internal combustion engine; and injecting an amount of a secondary fuel based on a fraction of less than 15% of the measured quantity of the primary fuel, the primary fuel having a larger molecular structure than the secondary fuel.